Combination process of isomerization and a sorption process followed by selective frationation



8 2 5. 6 6 oww zmN a s RO Rs 0I Vl ST Nv 0n Am Mm E Mm wf m mmv Vl m Nummm /q A T T wwwa. j J. v Emu w m 0 SEQ@ Amsw a a a H YN U. U. W. vr..wad 0 w 1 m B V De U D D wn W W w. EOF 0 J Z xbxbqmm, m0 *m F ww Q. N0mm. Nv 4 N.\ m. wm A C l 1. /I l.' /lv nbxl mm, l1 7 m. N 9m -1 4 T/ fA D f /m n m 52m mm|\ Qnl ml COMBINATION PRGCESS F ISOMERIZATION AND ASORPTION PROCESS FOLLOWED BY SELECTIVE FRACTIONATION Vladimir Haensel,Hinsdale, Ill., assigner, by mesne assignments, to Universal UilProducts Company, Des Plaines, lll., a corporation of Delaware FiledNov. 8, 1957, Ser. No. 695,292

3 Claims. (Cl. 260-666) This invention relates to a process forproducing a hexane having a high octane number from a mixture of C5parain and naphthene feed stock. More particularly, this invention isconcerned with a combination process whereby an isomerization reactionzone efuent is introduced into a sorption process wherein low octanenumber normal hexane is removed and followed with selectivefractionation of the remaining eluent so that the desired high octanenumber hexanes are obtained.

Normal parafns find use as intermediates fo-r raw materials in theproduction of many petrochemical oompounds and these same normal paransalso nd wide use as solvents. While normal paraflins are notparticularly desirable as a motor fuel, because of their relatively lowoctane numbers, they may be isomerized readily to -isoparaffms whichhave substantially higher octane nurnbers. Since isomerization is anequilibrium reaction, it is preferred that isoparaffins be separatedfrom normal paratflns before subjecting the normal parains toisomerization. In this manner, more of the normal hexane can beisomerized than would take place in the presence of isoparains. ln thepresent process the normal hexane is removed from the fractionationproduct thereby increasing the octane number of the combination processhexane product. The normal hexane separated from the fractionationresidue is subjected to further treatment in the isomerization reactionzone to convert them to isoparains of higher octane number.

It is an object of the present invention to subject a mixture of C6paraflins and naphthenes to isomerization, a sorption process wherebynormal hexane may be separated from the isomerization reaction zoneeffluent, and follow this with selective fractionation of the branchedchain hexanes and cycloparains so that a high octane number product isobtained. It is also an object of the present invention to provide asorption zone with a means whereby the sorbed normal hexane may berecycled to the isomerization reaction zone for the conversion t0 higheroctane number hexanes.

`In one embodiment this invention relates to a process for producing ahexane having a high octane number from a C6 parain hydrocarbon feedstock which comprises subjecting said feed stock to isomerization in thepresence of an isomerization catalyst at isomerization conditions withina reaction zone, contacting resulting isomerization reaction zoneproduct with a solid sorbent in a sorption Zone to effect the selectivesorption of the normal hexane component of the isomerization product andthe selective rejection of branched chain hexanes and cycloparalins,separately withdrawing from the sorption zone a stream comprising aproduct having an octane number greater than said feed stock, separatelycontacting spent sorbent with a desorbent stream comprising a normalparaffin of at least 4 but less than 6 carbon atoms per molecule,recovering a desorbed eiluent comprising normal hexane and passing thelatter to said isomerization reaction zone, passing the rejected hexanesto a rst fractional distillation zone, separating therefrom a rst f2,966,528 Patented Dec. 27, 1960 overhead comprising dimethylbutanes,subjecting the residue of said rst fractional distillation to a secondfractional distillation zone and therein separating an overheadcomprising monomethylpentanes, recycling said last mentioned overheadproduct to said isomerization reaction zone, and recovering a seconddistillation residue comprising branched chain and cyclic C6hydrocarbons from the bottom of said second fractionation zone.

in another embodiment the present invention relates to a process forproducing a hexane having a high octane number from a mixture of C6paraflns and naphthenes feed stock which comprises subjecting said feedstock to isomerization in the presence of an isomerization catalyst atisomerization conditions within a reaction zone, passing the resultingisomerization reaction product to a debutanizer column wherein lowboiling hydrocarbon gases are passed overhead, contacting the resultingresidue of said debutanizer column with a solid sorbent in a sorptionzone to effect the selective sorption of the normal hexane and theselective rejection of the branched chain hexanes and cycloparains,separately withdrawing from the sorption zone a stream comprising thethus rejected hydrocarbon having an octane number greater than said feedstock, separately contacting spent sorbent with a desorbent streamcomprising a normal paraffin of at least 4 but less than 6 carbon atomsper molecule, recovering a desorbed effluent comprising normal hexaneand passing the latter to said isomerization reaction zone, passing therejected hydrocarbon to a tirst fractional distillation zone, separatingtherefrom a first overhead cornpris-ing dimethylbutanes, subjecting theresidue of said first fractional distillation to a second fractionaldistillation zone and thereby separating an overhead comprisingmonomethylpentanes, recycling said last mentioned overhead to saidisomerization reaction zone, and recovering a second distillationresidue comprising branched chain and cyclic C6 hydrocarbons from thebottom of said second fractionation Zone.

In the operation of catalytic reforming processes, it has been observedthat the product, usually called reformate, contains a small amount ofnormal paraffin having -a relatively low octane number. The presence ofthese paratins is due to the fact that under operating conditions ofreforming, equilibrium concentration represents a fair concentration ofnormal paratiins. The presence of these normal paratlins in thereformate causes a substantial depreciation of the octane number of thereformate.

As reforming processes are' operated to obtain a conversion of thesenormal paratiins into aromatics or into higher octane number branchedchain and lower boiling parafns during the reforming reaction, it hasbeen found that the yield-octane number improvement relationship is suchthat somewhat more than one yield percent is lost for each octane numbergained in the range of octane numbers in the order of -95 F-l clear.This is due to the conversion of normal liquid components into normallygaseous components. However, if the normal parains were removed from thereformate the octane number would improve more favorably, for example, areformate having an octane number of 85 F-l clear and containing 10%normal paraffin, having an average octane number of 0, would have anoctane number improvement of 85 to 94.5 on the strictly arithmeticalblending basis. In the present process the octane number of theisomerization reaction zone eluent is increased through the use of asorption process whereby normal paraliins are sorbed and the branchedchain hexanes and cycloparains are rejected and said hydrocarbons arethen selectively fractionated to produce high octane number branchedchain hexanes and cycloparains. The normal hexane is subjected to adesorbent 3 Stream comprising a normal paraffin of lat least 4 but lessthan 6 carbon atoms per molecule and said normal hexane is returned tothe isomerzation reaction zone as recycle to be further isomerized tohigher octane number hexanes. The contact of the normal hexane,cycloparains and branched chain hexanes in the sorption zone is with asolid sorbent which has a selective sorbing power for normal hexane. Thecontact is for a time suicient to sorb a substantial amount of thenormal hexane present in the charge to the sorption zone. The sorptiontower is maintained at a temperature and pres- Sure so that the chargeis maintained in the liquid phase. It is preferred to maintain thetemperature in the sorption zone substantially within the range of fromabout 80 C. to about 152 C. The pressure in the sorption zone is withinthe range or from about 13.5 to about 68 atmospheres such that thecharge is kept in the liquid phase.

Any solid sorbent material which has a high power of selectively sorbingnormal paraiiins from their mixtures with other hydrocarbons may be usedin the present process. Crystalline metal alumino-silicates, such ascalcium alumino-silicate, strontium alumno-silicate, bariumalumino-silicate, and potassium alumino-silicate are suitable sorbentsto be used although they do not necessarily provide quantitatively thesame results. Crystalline calcium alumina-silicate, which has beenheated to remove the water of hydration, is preferred. These crystallinecalcium alumino-silicates which have been heated to remove the water fhydration have pore diameters of about 5.1 A. units; this diameter isslightly larger than the calculated critical diameter but somewhatsmaller than the critical diameter of isoparains, cycloparaffins andaromatics. Thus, it is possible to sorb normal par- `aflins from themixture of branched chain and cyclic paraiiins.

The contact of the charge with the solid sorbent is for a time suicientto sorb substantial quantities of the normal paraiiin from the charge.After a substantial quantity of the normal paratin is sorbed, the sorbednormal parain is removed and recovered from the solid sorbent andsubsequently returned as recycle to the isomerization reaction zone forfurther conversion to high octane number isoparains.

The usual procedure for the removal ot' the sorbed normal paraflins fromthe solid sorbent is heating under vacuum. Such a procedure involves aconsiderable expenditure with respect to both initial installation andoperating cost. The present invention provides for a simple and in itspreferred embodiment essential isothermal operation of the sorptioncycle. This results in a great saving in operating cost and theequipment necessary for the operation is simple and readily available.

The accompanying drawing illustrates diagrammatically the process owembodying the present combined process for producing high octane hexanefractions. Also in referring to and describing the drawing, aSkellysolve B was utilized as the charge stock, said charge having aninitial boiling point of 150 F. and an end boiling point of 175 F. andcontaining 48% by weight normal hexane. The charge stock was passedthrough line 1 and commingled with a monomethylpentane recycle stream 3and a normal hexane recycle stream 4, the source of these latter twostreams will be subsequently described. The charge stock, amonomethylpentane stream and a normal hexane stream are combined with ahydrogen recycle gas stream 2 and then passed to an isomerzationreaction zone 5 containing isomerization catalyst.

The conditions utilized in reaction zone 5 will depend upon theparticular isomerzation catalyst utilized therein. The preferredcatalyst in ,the process of this invention is one comprising a platinum.group metal, particularly platinum, combined halogen, and alumina. Withsuch acatalyst, the pressure utilizedin the reaction zone will rangefrom about to about 1000 pounds per square inch, the temperature willrange from about 100 C. to about 450 C. and the liquid hourly spacevelocity will range from about 0.1 to about 10. The hydrogen tohydrocarbon ratio in the reaction zone will range from about 0.25 toabout 5 mols of hydrogen per mol of hydrocarbon. When the catalystutilized comprises platinum, alumina, and combined chlorine in an amountof from about 2.5 to about 8.0 weight percent of the latter, thereaction zone temperature will be lower than the higher part of theabove set forth range, for example, from about C. to about 250 C. Insome instances it is desirable and/or advisable to utilize hydrogenhalide along with these catalysts and thus the use of hydrogen chloride,for example, is within the generally broad scope of the presentinvention.

The isomerzation reaction zone 5, when being charged with the abovementioned Skellysolve B charge stock is operated at a pressure in theorder of 900 p.s.i.g. and a temperature of about 150 C. with a liquidhourly space velocity of 0.5 and a hydrogen to hydrocarbon ratio in thereaction zone of the order of 6.0. The isomerzation catalyst containedin said isomerzation reaction zone 5 comprises platinum, alumina, andcombined chlorine, in an amount of the order of 5.5 weight percent ofthe latter along with a continuous addition of hydrogen chloride to saidisomerzation reaction zone 5.

An isomerzation reaction zone effluent is withdrawn from saidisomerzation reaction zone 5 by means of line 6 and passed to aseparation zone 7 wherein a separation of hydrogen from hydrocarbons iseffected. A relatively high purity hydrogen recycle gas stream iswithdrawn from the top of said separation zone 7 by means of line 2 ands joined with a hydrogen gas makeup stream 8 and said total recyclehydrogen gas is passed to isomerzation reaction zone 5 as hereinbeforedescribed. A hydrocarbon effluent stream containing of the order of 12%by weight normal hexane is withdrawn from the bottom of separation zone7 by means of line 9 and passed to a conventional debutanizer column 10wherein low boiling hydrocarbon gases, in particular isobutane andnormal butane, are passed overhead by means of line 11 for subsequentuse in a sorption zone hereinafter described. A residue product iswithdrawn from the bottom of debutanizer column 10 by means of line 12and passed to a sorption zone. The normal hexane, branched chain hexanesand cycloparal'lns in line 12 are passed through either sorption zone 19or sorption zone 20. In this illustration it will be considered that thecharge from line 12 was previously directed to sorption zone 20 and nowthe charge is being passed into sorption zone 19. Valve 16 in line 15 isclosed and valve 14 in line 13 is open. The hexane mixture from line 12continues through line 13, valve 14, and line 17 to sorption zone 19. Insorption zone 19 the hexane mixture is contacted with a crystallinecalcium alumino-silicate which had previously been heated to remove thewater of hydration. This sorption zone material sorbs normal hexane fromthe hexane mixture and allows the branched chain hexanes andcycloparains to pass from the sorption zone 19 through line 21. Thissorption zone is maintained at a temperature of the order of 156 C. andat a pressure of the order of 37.5 atmospheres. The liquid hourly spacevelocity is of the order of 1.0, that is, the volume of liquidhydrocarbon charged per volume of sorption material per hour. The eluentfrom sorption zone 19 when withdrawn through line 21 has a decreasednormal hexane content when compared with the charge in line 12. Thematerial in line 21 continues through line 23 containing open valve 25and then through line 37.

The material in line 37 consists predominately of the branched chain andcyclic hexanes and is passed to a rst fractionation zone 38 for furtherfractionation so tha the high octane number hexanes are obtained.

After a period of operation on this sorption cycle, the

sorption material in sorption zone 19 has picked up a substantial amountof normal hexane. For the purposes of this illustration it will beconsidered that the charge in line 12 was passed through sorption zone20 previously and. that, therefore, the solid sorption material in zone20 has a substantial amount of normal hexane sorbed thereon. v

A normal liquid butane stream from a source other than the processitself will be used in illustrating the desorbing step of the process.Valve 46, line 43 is maintained closed while valve 45 in line 11 isopened so that the overhead product from the conventional debutanizingzone is discharged from the process as a product stream of said process.The liquid normal butane stream is introduced into line 36 containingopen valve 44 where said liquid normal butane stream flows through line43. Valve 26 in line 27 and valve 16 in line 15 are maintained in aclosed position and the normal butane stream flows from line 43 throughvalve 35 in line 33 and then through line 18 into sorption zone 20.Valve 34 in line 32 is maintained closed during the desorption cycle ofsorption zone so 'that the normal butane stream does notflow intosorption zone 19. This liquid normal butane displaces the normal hexanesorbed on the crystalline calcium alumino-silicate. During thisdesorbing operation chamber 20 is maintained at a temperature of theorder of 156 C. and at a pressure of the order of 37.5 atmospheres. Theeiuent from chamber 20 which is withdrawn through line 22 during thisdesorbing operation contains predominately normal hexane hydrocarbons.The ow of liquid normal butane into chamber 20 through line 18 iscontinued until substantially all of the normal hexanes are displacedfrom the solid sorbent. The normal hexanes continue through line 28containing open valve 30, and then into line 4 which returns the normalhexane as recycle to the isomerization reaction zone hereinabovedescribed. Normal hexane is subsequently isomerized to the higher octanenumber isohexanes in the isomerization reaction zone 5. When the normalhexane has been subsequently displaced from the solid sorbent in chamber20 by the liquid normal butane, the pressure on chamber 20 is reduced to20.4 atmospheres, hereby vaporizing the liquid normal butane in thischam- A convenient source for the liquid normal butane used in thedesorbing step of the sorption zone is overhead product 11 from theconventional debutanizer 10. When the overhead product 11 is to be usedin the desorbing step, valve 45 in line 11 and valve 44 in line 36 areclosed while valve 46 in line 43 is maintained open. The liquid butanestream from column 10 passes through line 11 and open valve 46 in line43 and then into the sorption zone of the process. Any other source ofthe liquid normal butane which may be readily available can also be usedin the desorption step.

After this desorbing operation the charge in line 12 may be introducedinto chamber 20 and a desorbing operation started on chamber 19. Thismay be accomplished by closing valve 35 in line 33 and closing valves 14and 25 and opening valves 16 and 26. In this operation the charge passesthrough line 15, open valve 16, and line 18 into sorption zone 20. Theeffluent from sorption zone 20 continues through line 22 containing openvalve 26 and then into line 24 which allows the rejected branched chainhexanes and cycloparains to flow into line 37 and then into a firstfractionation zone 38. Further fractionation of the rejected hexanes isaccomplished in a first fractionation zone 38 to produce high octanenumber hexanes, the steps involved in this further fractionation will behereinafter described.

Sorption zone 19 is now ready for the desorption cycle. Chamber 19 isplaced on the desorption cycle by closing valves 14, 35, 30, and andopening valves 34 and 29. In this desorption cycle valve 46 in line 43is closed while valve 45 in line 11 is open so that the overhead productfrom theA conventional debuta'riizer 10 is dis# charged from the processas a product stream. The liquid normal butane stream is introduced intoline 36 containing open valve 44 from where said liquid normal butanestream flows to line 43. The liquid normal butane in line 43 is passedto open valve 34 in line 32 and then into line 17 which introduces saidliquid normal butane into sorption zone 19. The effluent which compriseschiefly normal hexane during the desorption cycle, is withdrawn throughline 21, continues through line 31 containing open valve 29 and theninto line 4. 'Ihe normal hexane in line 4 is subsequently recycled toisomerization reaction zone 5 for further isomerization to the higheroctane number hexanes. is reduced on zone 19 so as to vaporize theliquid normal butane, zone 19 is again ready for a sorption cycle.

The rejected branched chain hexanes and cycloparaffins in line 37 arepassed to a first fractionation zone 38. A high octane number productcontaining dimethylbutanes is passed overhead from said firstfractionation zone 38 by means of line 39, while a residue product isWithdrawn from the bottom of said irst fractionation zone 38 by means ofline 40 and passed to a second fractionation zone 41. A low octanenumber monomethylpentane fraction is removed in said secondfractionation zone 41 and passed overhead by means of line 3 and thenrecycled to said isomerization reaction zone 5 as hereinbefore describedfor further isomerization to higher octane number hexanes. A residueproduct containing methylcyclopentane and cyclohexane is withdrawn fromthe bottom of said second fractionation zone 41 by means of line 42 andcombined with the dimethylbutanes contained in line 39 to form a highoctane number hexane product.

In the above illustration the combination process of this invention hasbeen set forth. As stated hereinabove the combination of isomerization,a sorption process and selective fractionation are combined to produce ahigh octane number hexane product by the removal of normal hexane fromthe product stream. It is also illustrated that the normal hexane, whenwithdrawn from the product stream, is returned for further isomerizationalong with monomethylpentanes to an isomerization reaction zonecontaining an isomerization catalyst.

I claim as my invention:

1. A process for producing a hexane having a high octane number from afeed stock mixture of C6 parafiins and naphthenes which comprisessubjecting said feed stock mixture of C6 paraflins and naphthenes toisomerization in the presence of an isomerization catalyst atisomerization conditions within a reaction zone, debutanizing theresulting isomerization reaction zone product and thereafter contactingthe latter with a solid sorbent in a sorption zone to effect theselective sorption of the normal hexane component of the isomerizationproduct and the selective rejection of branched chain hexanes andcycloparaffins, separately withdrawing from the sorption zone a streamcomprising the thus rejected hydrocarbon stream having an octane numbergreater than said feed stock, separately contacting spent sorbent withliquid butane from the debutanizing step to remove said normal hexanecomponent from the spent sorbent, recovering a desorbed efiluentcomprising normal hexane and passing the latter to said isomerizationreaction zone for isomerization treatment therein together with saidfeed stock mixture, passing the rejected hydrocarbon stream to a firstfractional distillation zone, separating therefrom a first overheadcomprising dimethylbutanes, subjecting the residue of said firstfractional distillation to a second fractional distillation zone andthereby separating an overhead comprising monomethylpentanes, recyclingsaid last mentioned overhead to said isomerization reaction zone, andrecovering a second distillation residue comprising branched chain andcyclic C5 hydrocarbons from the bottom of said second fractionationzone.

After the pressure -Y essere@ 2. The process of claim 1 furthercharacterized in that the overhead product from the first fractionaldistillation zone is combined with the rejected branched Y,chain hexanesand cycloparains from the sorption zone to Aform a high octane numberhydrocarbon product.

3. A process for producing a hexane having a high octane number from afeed stock mixture o f C6 parans and naphthenes which comprisessubjecting said feed stock mixture of C6 parains and naphthenes toisomerization in the presence of an isomerization catalyst atisomerization conditions within a reaction zone, passing the resultingisomerization reaction zone product to a debutanizer column and thereinseparating butane from said product, contacting the resulting residue ofsaid debutanizer column with a solid sorbent in a sorption zone toeffect the selective sorption of the normal hexane component and theselective rejection of the branched chain hexanes and cycloparafns,separately withdrawing from the sorption zone a stream comprising therthus rejected hydrocarbon stream having an octane number greater thansaid feed stock, separately contacting spent sorbent with liquid butanefrom said debutanizer column to remove said normal hexane componentffrom the spent sorbent, recovering a desorbed efliuent comprisingnormal hexane and passing the latter to said isomerizationReferences-Cited in the le of this patent UNITED STATES PATENTS2,395,022 Sutton et al Feb. 19, 1946 2,396,331 Marschner Mar. 12, 19462,425,535 Hibshman Aug. 12, 1947 2,766,302 Elkins Oct. 9, 1956 2,818,449Christensen et al. Dec. 31, 1957 2,818,455 Ballard et al. Dec. 31, 19572,859,173 Hess et al. Nov. 4, 1958 2,909,582 Bleich et al. Oct. 20, 1959und

1. A PROCESS FOR PRODUCING A HEXANE HAVING A HIGH OCTANE NUMBER FROM AFEED STOCK MIXTURE OF C6 PARAFFINS AND NAPHTHENES WHICH COMPRISESSUBJECTING SAID FEED STOCK MIXTURE OF C6 PARAFFINS AND NAPHTHENES TOISOMERIZATION IN THE PRESENCE OF AN ISOMERIZATION CATALYST ATISOMERIZATION CONDITIONS WITHIN A REACTION ZONE, DEBUTANIZING THERESULTING ISOMERIZATION REACTION ZONE PRODUCT AND THEREAFTER CONTACTINGTHE LATTER WHICH A SOLID SORBENT IN A SORPTION ZONE TO EFFECT THESELECTIVE SORPTION OF THE NORMAL HEXANE COMPONENT OF THE ISOMERIZATIONPRODUCT AND THE SELECTIVE REJECTION OF BRANCHED CHAIN HEXANES ANDCYCLOPARAFFINS, SEPARATELY WITHDRAWING FROM THE SORPTION ZONE A STREAMCOMPRISING THE THUS REJECTED HYDROCARBON STREAM HAVING AN OCTANE NUMBERGREATER THAN SAID FEED STOCK SEPARATELY CONTACTING SPENT SORBENT WITHLIQUID BUTANE FROM THE DEBUTANIZING STEP TO REMOVE SAID NORMAL HEXANECOMPONENT FROM THE SPENT SORBENT, RECOVERING A DESORBED EFFUENTCOMPRISING NORMAL HAXINE AND PASSING THE LATTER TO SAID ISOMERIZATIONREACTION ZONE FOR ISOMERIZATION TREATMENT THEREIN TOGETHER WITH SAIDFEED STOCK MIXTURE, PASSING THE REJECTED HYDROCARBON STREAM TO A FIRSTFRACTIONAL DISTILLATION ZONE, SEPARATING THEREFROM A FIRST OVERHEADCOMPRISING DIMETHYLBUTANES, SUBJECTING THE RESIDUE OF SAID FIRSTFRACTIONAL DISTALLATION TO A SECOND FRACTIONAL DISTILLATION ZONE ANDTHEREBY SEPARATING AN OVERHEAD COMPRISING MONOMETHYLPENTANES, RECYCLINGSAID LAST MENTIONED OVERHEAD TO SAID ISOMERIZATION REACTION ZONE, ANDRECOVERING A SECOND DISTILLATION RESIDUE COMPRISING BRANCHED CHAIN ANDCYCLIC C6 HYDROCARBONS FROM THE BOTTOM OF SAID SECOND FRACTIONATIONZONE.